I have thought that through nursing, your baby and your body are setting the pace for when the right time for another baby is, if that makes sense, but of course, its much more complicated than that. if you are not ready to wean yet, then your cycle will not return.
I hear you about ambivalence though....and it is so hard. I am ambivalent too. I want another baby, and I want to be pregnant soon. But, my relationship with my partner needs attention, my baby is a very active one year old which makes me think that the two's may be tough and need my patience and focus solely, and our donor is not available.